1. Field of the Invention
The present invention relates to a printing apparatus and a printing method using the printing apparatus and more particularly to a printing apparatus and a printing method which use a print head having a plurality of print elements or nozzles which are arranged to differ in nozzle array number and nozzle interval according to a colorant to be ejected.
2. Description of the Related Art
As personal computers, word processors and facsimiles have come into widespread use in offices and homes in recent years, increasing varieties of printing apparatus are being proposed as information output devices for these equipment. Of these, ink jet printers can relatively easily deal with a color printing using a plurality of different inks. The ink jet printing apparatus has many advantages, such as small operation noise, a capability of printing high quality images on a variety of kinds of print mediums and small size. This type of printer therefore is suited for office and home use. Of the ink jet printing apparatus, a serial type printing apparatus, that scans a print head over a print medium to print an image, is in wide use today because of its ability to form high quality images at low cost.
For the low-cost serial type printing apparatus, however, there is a growing demand for an enhanced printing performance. Representative factors of printing performance include image quality and printing speed.
One factor determining an image quality is a kind of ink. Generally, a high quality printing can be achieved by increasing the number of inks used and selecting appropriate kinds of inks. The kind of ink can be distinguished by colorant used in ink, ink color, ink density and others. Among coloring materials for use in ink are, for instance, dye ink and pigment ink. As for the density, there are dark and light inks. As for the ink color, there are orange, red and blue as well as three primary colors for printing of cyan, magenta and yellow.
For example, a well-known printer uses six kinds of inks, such as a dye black ink, a dye yellow ink, dark and light dye magenta inks, and dark and light dye cyan inks, and another uses four kinds of inks, such as a pigment black ink, a dye yellow ink, a dye magenta ink and a dye cyan ink. The former is intended to output with high quality a photographic image from a digital camera or scanner on a glossy print medium and the latter is intended to output with high quality black characters of documents and black lines of tables on plain paper.
Another factor that determines a printed image quality is a resolution. Generally, printing at a higher resolution tends to enhance the quality of printed image. For example, in the case of black characters, printing at a high resolution smoothes edge portions resulting in a higher quality of printed image. In the case of color images, too, the number of grayscale levels that can be represented in one pixel is one of factors determining the image quality. A higher resolution can realize a greater number of tones for one pixel, producing a higher quality of printed image.
Thus, even with two printing apparatus that use the same combination of inks for printing, printed results may differ if the resolutions are different. Realizing a higher resolution is important in producing a higher quality of printed resulted.
Inventions have been made concerning print heads capable of dealing with a plurality of resolutions. Japanese Patent Application Laid-open No. 7-186411 (1995) discloses an ink jet printer with a print head having a plurality of print resolutions. This print head has different resolutions for monochrome printing and color printing, with a resolution for black ink set higher than those of color inks. In a printed document having a combination of texts and images, a black component that appears most frequently in a text part of the document is printed at a high resolution to improve the overall quality of a printed image.
Japanese Patent Application Laid-open No. 8-258291 (1996) discloses an invention about a print head that ejects ink droplets of different dot sizes corresponding to a plurality of resolutions. The technique disclosed here combines small black ink dots and large color ink dots in many ways as the print head ejects ink.
In an ink jet printing apparatus, printing at a higher resolution means an increased number of ink dots that can be printed in a predetermined area. Therefore, where the printing apparatus uses many ink colors and ink kinds, if a high-resolution printing is performed for all ink colors, a huge volume of data needs to be handled. As a result, a storage area to hold ejection data and other associated information becomes necessarily large, requiring a large memory capacity in the printing apparatus, which in turn raises the cost of apparatus. Furthermore, the time taken to map the ejection data and the time required to transfer the data to a head driver increase, raising a variety of problems, such as an increased manufacturing cost of the printing apparatus and a prolonged printing time.
In the print head manufacturing technology, as the print resolution increases, an interval between nozzles making up the print head must be reduced. However, manufacturing the nozzles at a higher density requires a sophisticated manufacturing technology and a faulty product occurrence probability increases. This means that manufacturing a print head integrated with a high density of nozzles itself will result in an increase in the production cost.